Which term describes the amount of a drug that reaches systemic circulation?

Which term describes the amount of a drug that reaches systemic circulation?

• A. Bioavailability
• B. Efficacy
• C. Potency
• D. Tolerance

Answer: (A)

Bioavailability is the fraction of an administered dose that reaches systemic circulation in active form. It matters because it tells you how much drug is actually available to have an effect after a given route and formulation. For example, intravenous administration delivers nearly all of the drug into the bloodstream, while oral dosing often results in less reaching circulation due to incomplete absorption and first-pass metabolism in the liver. This concept focuses on how much drug becomes available systemically, not on the intensity of effect. Efficacy describes the maximal effect a drug can produce, potency refers to the amount needed to achieve a given effect, and tolerance is the diminished response that develops with repeated use. Therefore, bioavailability best describes the amount of drug that reaches systemic circulation.

Bioavailability is the fraction of an administered dose that reaches systemic circulation in active form. It matters because it tells you how much drug is actually available to have an effect after a given route and formulation. For example, intravenous administration delivers nearly all of the drug into the bloodstream, while oral dosing often results in less reaching circulation due to incomplete absorption and first-pass metabolism in the liver. This concept focuses on how much drug becomes available systemically, not on the intensity of effect. Efficacy describes the maximal effect a drug can produce, potency refers to the amount needed to achieve a given effect, and tolerance is the diminished response that develops with repeated use. Therefore, bioavailability best describes the amount of drug that reaches systemic circulation.